Entertainment overload, that's what it is. Long before the net became so all-pervasive, gripped us by the throats and refused to let go, I'd keep on dipping into my meagre Amiga games collection even if I was bored witless with the games. I didn't have an endless supply of new releases I could flit between because they were harder to come by - you'd have to actually leave the house and visit friends to swap disks, send off for pirate copies and wait for them to arrive in the post or buy them legitimately (I did my fair share of that too). I kept re-visiting old games because the alternative was to sit around in the local park with a friend and bleat, "I'm bored, what should we do now?". Eyes glazed over he'd wearily reply, "I'm more bored than you", but wouldn't offer any solutions. Trying to avoid that situation always led us back to the computer. If I plugged away at a game for long enough I'd progress a stage further and that would extend its life. I'm not saying the only thing that made old school games successful was a lack of alternative forms of entertainment, just that they may have failed to gain such a firm foothold in my consciousness under different circumstances.
These days it's too tempting for kids to ditch a game if they fall at the first hurdle - there are so many other games out there vying for their attention which may be better than the current one they're playing, or at least provide a more instantaneous pay-off. That's just games - game programmers also have to compete with easy access to new movies, instant messengers, web sites and so on. In this climate you really have to wow someone to capture and hold their attention. Enter very pretty, but ultimately shallow and soulless 3D graphics *yawn*.
You've also got to take the nostalgia factor into account. People aren't going to play your game and get all gooey-eyed over it as it's brand new to them, even if it's retro by design. I think we cut older games much more slack precisely because we were so bowled over by them on our first encounter. We play them today and our opinions are coloured by our original impressions. If near-identical games were released today under a slightly different guise I don't think they'd get such a warm reception from the people who adored the originals. I don't doubt that some classics stand the test of time exceptionally well (I wouldn't still be talking about them here otherwise), but there's no denying that times have changed and there's no going back. You could say that the bar has been raised ...or crookedly realigned by a generation of spoilt brats with ADHD.